The present invention relates to a method of making a filled tubular article for controlled insertion into a molten metal as it is being cast, and to the article made thereby.
The addition of alloying and treating agents into a molten metal such as iron, by insertion of an elongated rod-like article into a casting mold's downsprue is becoming more well known in the art. More sophisticated methods and apparatuses have recently been developed to controllably insert filled tubular articles into the casting molds during metal pouring at exactly the rate and point required to obtain the desired castings. These elongated articles usually have a core of powdered ingredients or particulate material carried in a protecting tube. As far as is known, such articles are manufactured by depositing the powdered ingredients onto a strip of metal that may be partly formed into a trough. The strip is thereafter formed into a tube by conventional methods with the edges either abutting or overlapping. Unfortunately, a major problem is experienced at this point because the ingredients of the core are not sufficiently densified within the tube which results in the powder tending to separate and move within the tube. Consequently, it has been found necessary to pass the tube axially through a forming die which reduces its external diameter and compacts the powdered ingredients. Even with this extra step it is a frequent practice to crimp or pinch the ends of the tubes to keep the particulate material from falling out. Such crimping practice is also used for retaining powder in an alternate construction embodying short stiff tubes which are filled with powder after the tubes are made.
Not only are the aforementioned manufacturing procedures for making the filled tubes complicated, but also it has been found that the thickness of the tubes is often excessive or irregular, and therefore the volumetric ratio or proportion of the core material to the entire article is disproportionately low. For example, if attempts are made to make the radial thickness of the metal tubes below approximately 0.25 mm with current technology then the edges of the tubes generally fail to remain in abutment and this allows powder to fall out. On the other hand, if the tube edges are overlapped, when the rod is inserted into a molten bath the melting rate around its periphery is unequal. Because of the relatively poor dissolution or melting rate of the relatively thick prior art tubes, the rate of feeding them into the molten bath has necessarily been reduced in order to prevent the unmelted and excessively stiff remaining portions of the tubes from penetrating the sides of the casting mold's downsprue.
In view of the above, it would be advantageous to replace the relatively thick and non-uniform prior art tubes with a thinner casing, and yet retain a relatively high degree of uniformly dense fill material within the core.